A sensor may be a sound sensor, that is to say a microphone, a temperature sensor, a pressure sensor or a gas sensor, for example. Today, many apparatuses have sensors for capturing their surroundings. By way of example, mobile phones, tablet computers, handheld computers, laptops and/or screens have small microphones, e.g. miniaturized microphones. Other apparatuses, such as domestic appliances or motor vehicles, for example, also regularly have sensors, however, for example temperature sensors, pressure sensors or gas sensors.
Various operating currents regularly flow in such sensors, for example for initializing a measurement, for performing a measurement and/or for transmitting a value that is representative of the correspondingly captured measured variable. The operating currents can impair and/or corrupt the quality of the measurements, however. By way of example, the applicable sensors or at least subregions of the sensors are unintentionally heated by means of the operating currents, as a result of which the applicable measurement results can be influenced. Apart from the operating currents that are variable over time, base currents that are constant over time can also flow in the sensors, for example for maintaining a standby mode. The constant base currents contribute to constant heating of the sensors. The operating currents and the base currents together form the total operating currents of the sensors.
Conventional microphones, for example, in particular miniaturized microphones, frequently each have a microsystem (MEMS) having a diaphragm, have an analogue-to-digital converter, an amplifier and/or an integrated circuit and an interface for communication with an apparatus that is external to the microphone, and also optionally a temperature sensor. The diaphragm, together with an electrically conductive plate, forms a capacitor in the microphone. The diaphragm is used to pick up pressure vibrations and/or sound vibrations that cause the diaphragm to vibrate in a corresponding manner. On account of the vibrating diaphragm, a distance between the diaphragm and the plate changes, which results in an inversely proportional capacitance change that can be evaluated by an appropriate integrated circuit.
Optionally, the integrated circuit can amplify, modulate and/or otherwise alter the electrical signals. If need be, the analogue-to-digital converter can convert the analogue signal into a digital signal. The analogue-to-digital converter and the amplifier/impedance converter may be elements of the integrated circuit, for example. The integrated circuit can forward the possibly altered electrical signals via the interface to the apparatus that is external to the microphone. The optionally provided temperature sensor can be used to sense the temperature of the microphone and to take it into consideration when evaluating and/or further-processing the electrical signal of the microphone in order to be able to provide as good a sound pickup quality as possible.
During the operation of such a microphone, base currents that are fundamentally constant over time are used, but it is also possible for regularly changing operating currents to occur within the microphone. The constant base currents are used to provide the functionality of the microphone. The changing operating currents arise, inter alia, during a communication particularly between the microsystem and the integrated circuit, the integrated circuit and the interface and/or the temperature sensor and the integrated circuit using modulated currents that can be referred to as the operating currents, the information exchanged during the communication being encoded in the applicable modulation. In addition, some transmission forms and/or transmission protocols require one clock signal each in order to demodulate the modulated signal and to extract the information from the relevant signal.
The operating currents can lead to relatively fast heating of the microphone, e.g. of the microsystem and the diaphragm, and if the operating currents terminate abruptly, for example in the event of breaks in communication, then this can lead to relatively fast cooling of the microphone, e.g. of the microsystem and the diaphragm. Such a temperature change in the microsystem and e.g. in the diaphragm leads to deformation of the diaphragm and hence to a change of pressure in the pressure chamber that are registered by the microsystem and the integrated circuit as an electrical signal or at least as part of the electrical signal and cause low-frequency noise or else a sound in the output signal of the microphone that, if audible, is perceptible as hum.
In a comparable manner, it is also possible for operating currents in other sensors to influence the applicable measurement results. By way of example, operating currents occur in all sensors that are used for the communication of the sensors with applicable external apparatuses, e.g. for transmitting data that are representative of the captured measured values. Alternatively or in addition, it is generally possible for operating currents to arise that are used for the operation of the applicable sensor. By way of example, there are gas sensors that are heated during operation by means of various operating currents that can likewise have an adverse effect on measurement accuracy.